The present invention provides sintered cemented carbide bodies having increased resistance to plastic deformation comprising tungsten carbide (WC), a binder metal phase and one or more solid solution phases comprising at least one of the carbides, nitrides and carbonitrides of at least one of the elements of groups IVb, Vb and VIb of the Periodic Table of Elements. The present invention also provides a method for producing these sintered cemented carbide bodies. These sintered cemented carbide bodies are useful in the manufacture of cutting tools, and especially indexable cutting inserts for the machining of steel and other metals or metal alloys.
Sintered cemented carbide bodies and powder metallurgical methods for the manufacture thereof are known, for example, from U.S. Pat. Re. 34,180 to Nemeth et al. While cobalt has originally been used as a binder metal for the main constituent, tungsten carbide, a cobalt-nickel-iron alloy as taught by U.S. Pat. No. 6,024,776 turned out to be especially useful as a binder phase for tungsten carbide and other carbides, nitrides and carbonitrides of at least one of the elements titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, respectively.
Numerous attempts have been made in order to modify the properties or characteristics of the sintered cemented carbide bodies prepared by powder metallurgical methods. These properties include, but are not limited to, hardness, wear resistance, plastic deformation at increased temperatures, density, magnetic properties, resistance to flank wear and resistance to cratering. In order to provide cutting tools having improved wear properties at high cutting speeds, it is known, for example, that the sintered cemented carbide bodies should have increased contents of titanium or tantalum and niobium. On the other hand, however, it is known that increasing contents of titanium or tantalum or niobium result in a noticeable reduction of strength as they form solid solution carbides with tungsten carbide, since the amount of tungsten carbide-phase which provides for the maximum strength in a sintered cemented carbide body decreases with the formation of solid solution carbides.
Also well known to those skilled in the art is the fact that the addition of zirconium and hafnium increases the strength of sintered cemented carbide bodies both at room temperature and at higher temperatures. However, the increase in strength is combined with lower hardness and decreased wear resistance. In addition, a disadvantage of the addition of zirconium is its high affinity to oxygen and its poor wettability which impedes the sintering process used in the preparation of the sintered cemented carbide body.
U.S. Pat. Nos. 5,643,658 and 5,503,925, both hereby incorporated by reference herein, aim at improving hot hardness and wear resistance at higher temperatures of sintered cemented carbide bodies by means of adding zirconium and/or hafnium carbides, nitrides and carbonitrides to the powder mixture of tungsten carbide and a binder metal of the iron family. As a result thereof, the hard phases of at least one of zirconium and hafnium coexist with other hard phases of metals of groups IVb, Vb and VIb, but excluding zirconium and hafnium, with said hard phases forming, in each case, solid solutions with tungsten carbide. Due to the high affinity of zirconium for oxygen, either the starting powder materials have to be extremely low in oxygen, or the oxygen content has to be controlled by using a reducing sintering atmosphere.
JP-A2-2002-356734, published on Dec. 13, 2002, discloses a sintered cemented carbide body comprising WC, a binder phase consisting of at least one metal of the iron group, and one or more solid solution phases, wherein one of said solid solution phases comprises Zr and Nb while all solid solution phases other than the first one comprise at least one of the elements Ti, V, Cr, Mo, Ta and W, but must not comprise Zr and Nb. According to this Japanese patent document, the best cutting results are achieved at a tantalum content of less than 1% by weight of the total composition, calculated as TaC.
The present invention aims at achieving new sintered cemented carbide bodies having increased resistance to plastic deformation at increased temperatures and, as a result thereof, having increased wear resistance. Besides, the present invention aims at providing a powder metallurgical method of producing said sintered cemented carbide bodies. More specifically, it is an object of the present invention to provide a sintered cemented carbide body having at least two co-existing solid solution phases containing zirconium and niobium or one single homogenous solid solution phase containing zirconium and niobium.
Another object of the present invention consists in providing a method of producing said sintered cemented carbide body comprising the step of providing a powder mixture which upon sintering provides at least two co-existing solid solution phases or one single homogenous solid solution phase containing, in each case, zirconium and niobium, and providing improved sintering activity and wettability with hard constituents of elements of groups IVb, Vb, and VIb of the periodic table of elements.